CSS hacks as quite handy but it will work and save our time. But mostly I will prefer not to use hacks.

.example{
margin:0; /* This will work on all the browsers. FF3 */
_margin:0; /* This will work only on IE6 */
.margin:0; /* This will work only on IE7 */
}

Browser CSS Hacks

* IE 6 and below

* html {}

* IE 7 and Safari below

*:first-child+html {}

* IE 7 only

*:first-child+html {}

* IE 7 and modern browsers only

html>body {}

* Modern browsers only (not IE 7)

html>/**/body {}

* Recent Opera versions 9 and below

html:first-child {}